What to do if you misfuel your car

Matt Allan

According to RAC estimates, one driver every three minutes misfuels their car and a staggering 150,000 cars are filled with the wrong fuel every year.

It’s clearly an easier mistake to make than people imagine and it can come with repair bills running into thousands of pounds.

Making matters worse, while breakdown services and specialist recovery firms can help put it right, it’s unlikely that you’re insurance will cover the costs. A study last year by Defaqto found that 240 out of 300 policies specifically excluded misfuelling from their cover.

So what are the risks and what should you do if you misfuel your car?

Petrol in a diesel

An estimated 95 per cent of misfuelling errors are this way round as petrol fuel nozzles easily fit into the wider diesel filler necks.

The bad news is that as well as being the more common, it’s also the more serious mistake. If petrol is allowed to enter a diesel fuel system it can cause severe damage that’s incredibly expensive to put right.

Adding petrol to a diesel car is the more costly mix-up to make. Picture: Shutterstock

Diesel acts as a lubricant for the engine but petrol acts as a solvent, increasing friction and causing increased wear on components. Allowing petrol to enter the system can damage everything from the fuel pump and lines to the filters and injectors. The bill for cleaning and replacing components can easily run into four figures, with full engine rebuilds not unheard of.

If you have accidentally put petrol in your diesel tank the most important thing is not to start your car. Even turning the ignition is enough to prime the fuel pump and pull petrol into the system.

If you can, move your car away from the pumps but remember – don’t start the engine. If you can’t move it, ask the station attendant to use a cone or sign to advise other drivers the pump is out of action.

Call your breakdown provider or one of the many misfuelling specialists that exist. They will recover your car and complete the process of draining and flushing your fuel system.

If you’re lucky and haven’t started your car, this should take around 30 minutes to an hour and will cost £200-£300.

However, if you have started the engine it will need further investigation to assess any damage to sensitive components and carry out any repairs, so be prepared for a hefty bill.

Diesel in a petrol

Misfuelling could lead to the need for expensive diagnostic checks. Picture: Shutterstock

This is much less common as a diesel nozzle is larger than most petrol filler necks but it’s not unheard of and around five per cent of misfuelling is diesel being added to a petrol tank.

As with putting petrol in a diesel, the most pressing thing is not to start the engine and to seek professional help to recover the car and have its tank drained.

If you start the engine, the diesel will quickly fill the fuel system and coat the spark plugs. Your car will likely start to smoke and misfire. The engine may cut out after being started or might fail to start at all.

The damage is less serious than with a diesel but cleaning the system will still come with an expensive bill.

AdBlue in a diesel tank

An additional problem for modern diesel cars is the presence of an AdBlue tank. AdBlue is used to treat exhaust gases and reduce NOx emissions. However, the tank filler is often next to the fuel filler so mistakes are possible.

As with other misfuelling errors it’s vital that you don’t start your car. Allowing the additive into the fuel system and engine can cause costly damage so it’s important to follow the same process as any other misfuelling.

Avoiding misfuelling

The simplest way to avoid a big bill is to pay attention at the pump. Especially if you’re in a new car, or have borrowed someone else’s, it’s easy to pick up the wrong hose automatically. Always focus on what you’re doing and double check the car and the hose before starting fuelling.

Consider an aftermarket device that stops misfuelling. Ford helpfully builds in an Easy Fuel system to its cars but there are also aftermarket devices for diesel cars which prevent the narrower petrol nozzles from being inserted into the filler neck.